1. Field of the Invention
This invention relates to a photosensitive cell array for detection of non-visible light ray such as an X-ray, etc., and more particularly, to a method of fabricating a thin film transistor substrate for an X-ray detector that reduces the number of steps in an etching process using masks.
2. Discussion of the Related Art
Generally, imaging systems for photographing an object using non-visible light, such as an X-ray, etc., have been used for medical, scientific and industrial applications. These X-ray imaging systems typically convert the X-ray into an electrical signal and include an X-ray detecting panel for detecting an X-ray passing through an object.
As shown in FIG. 1, a conventional X-ray detecting panel includes a photosensitive layer 6 for detecting an X-ray and a thin film transistor substrate 4 for switching and outputting the detected X-ray from the photosensitive layer. The thin film transistor substrate 4 includes pixel electrodes 5 arranged in a pixel unit, and thin film transistors (TFTs), each of which is connected to a charging capacitor Cst, a gate line 3 and a data line (not shown). A dielectric layer 7 and an upper electrode 8 are provided on the upper portion of the photosensitive layer 6. The upper electrode 8 is connected to a high voltage generator 9. The photosensitive layer 6 is made of selenium with a thickness of hundreds of xcexcm. The photosensitive layer 6 detects an incident X-ray and converts it into an electrical signal. In other words, the photosensitive layer 6 produces an electron-hole pair when an X-ray is incident thereto and separates the electron-hole pair when a high voltage of several kV is applied to the upper electrode 8 by the high voltage generator 9. The pixel electrode 5 charges the charging capacitor Cst with holes produced by detection of an X-ray by the photosensitive layer 6. The thin film transistor produces a gate signal inputted over the gate line 3 to apply a voltage stored in the charging capacitor Cst to the data line. Pixel signals supplied to the data line are applied, via a data reproducer, to a display device.
FIG. 2 is a plan view showing a conventional structure of a thin film transistor substrate. In the thin film transistor substrate of FIG. 2, the pixel electrode 5 is formed at a unit pixel area defined by the gate line 3 and the data line 10. The charging capacitor Cst is formed by the pixel electrode 5 having a storage insulation layer (not shown) and a transparent electrode (not shown) at a lower portion of the pixel electrode 5. A ground electrode 22 is formed across the pixel electrode 5 to reset the residual electric charges of the charging capacitor Cst. The TFT is formed at an intersection between the data line 10 and the gate line 3 and consists of a gate electrode 12 extended from the gate line 3, a drain electrode 16 extended from the data line 10, a source electrode 14 connected to the pixel electrode 5 via a contact hole 15, and a semiconductor layer (not shown) connected to the source electrode 14 and the drain electrode 16. One end of the gate line 3 is provided with a gate pad 18. One end of the data line 10 is provided with a data pad 20. The gate pad 18 and the data pad 20 connect the gate line 3 and the data line 10 to a driver integrated circuit (IC), respectively. The gate line 3, the gate electrode 12 and the gate pad 18 are made of the same metal material and preferably have a structure in which aluminum (Al) and molybdenum (Mo) are sequentially disposed. The data line 10 is made from Mo to reduce its resistance value to produce good signal transfer characteristics. Like the gate pad 18, the data pad 20 has a structure with sequentially-disposed Al and Mo to connect to the driver IC using the aluminum wiring bonding. The data pad 20 is formed in a different layer from the data line 10. Therefore, the data pad 20 and the data line 10 are connected via a contact hole 19 formed through a gate insulating film. The gate pad 18 and the data pad 20 have aluminum layers which are exposed to be connected to the driver IC through the contact holes 17 and 21, respectively.
A method of fabricating the thin film transistor substrate having the structure as mentioned above is described with reference to FIG. 2 to FIG. 6. First, a metal film is formed on the glass substrate 2 using vapor deposition. Using a first mask pattern, gate line 3, a gate electrode 12, gate pad 18 and data pad 20 are formed simultaneously. In this case, the gate electrode 12, the gate line 3, the gate pad 18 and the data pad 20 have sequentially disposed aluminum (Al) 42 and molybdenum Mo 44 structure. Using continuous vapor disposition, a gate insulating film 32, an amorphous silicon layer and an amorphous silicon layer doped with an impurity, hereinafter referred to as xe2x80x9cn+ layerxe2x80x9d, are sequentially formed on the entire surface of the glass substrate 2 having the gate line 3 and the gate electrode 12, etc. Next, the n+ layer and the amorphous silicon layer is patterned using a second mask pattern to provide a semiconductor layer 34 forming a channel of the thin film transistor. After the semiconductor layer 34 is formed, the gate insulating film 32 on the data pad 20 is patterned using a third mask pattern so as to form an exposed region as a contact hole 19 to allow contact between the data pad 20 and the data line 10 to be formed later. In addition, the gate insulating film 32 on the gate line 3 is patterned by the same photolithography process using the third mask pattern, thus forming a contact hole (not shown) to allow contact between the gate line 3 and the data line 10 in a static electricity preventing circuit. After contact hole 19 is formed, a metal film of Mo material is formed and then patterned using a fourth mask pattern, thereby providing the data line 10, the source electrode 14, the drain electrode 16, and the ground electrode 22. In this case, the data line 10 is connected via the contact hole 19 to the data pad 20, as shown in FIG. 6. Likewise, in the static electricity preventing circuit, the data line 10 is connected, via the contact hole defined at the gate insulating film 32, to the gate line 3, as shown in FIG. 6. Subsequently, using a fifth mask pattern, a transparent electrode material is provided to form a first transparent electrode 35 for the charging capacitor Cst. After the first transparent electrode 35 is provided, a storage insulation film (i.e., dielectric layer) 36 for forming the charging capacitor Cst is provided. A transparent electrode material is then provided on the storage insulation film 36. The transparent electrode material is then etched using a sixth mask pattern to form a second transparent electrode 38. A protective film 40 is then formed. The second transparent electrode 38 serves as an etch stopper for limiting an etching depth of the protective film 40 when forming a contact hole through the protective film 40. In other words, the second transparent electrode 38 protects the storage insulation film 36 in a process of selectively etching the protective film 40 and the storage insulation film 36 when forming of the contact hole. After the second transparent electrode 38 is provided, the protective film 40 of an inorganic or organic material is formed on the entire surface and then patterned using a seventh mask pattern, thereby forming the contact hole 15 for connection between the source electrode 14 and the pixel electrode 5, the contact holes for connection between each of the gate pad 18 and the data pad 20 and the driver IC chip, and the contact hole for connection between the pixel electrode 5 and the second transparent electrode 38. The contact hole 15 for connection between the source electrode 14 and the pixel electrode 5 and the contact holes 17 and 21 for connection between each of the gate pad 18 and the data pad 20 and the driver IC chip are formed through the protective film 40 and the storage insulation film 36, as shown in FIG. 4 and FIG. 5. Consequently, a transparent electrode material is entirely coated and thereafter patterned using an eighth mask pattern, thereby providing the pixel electrode 5. After the pixel electrode 5 is provided, the Mo layers 44 exposed through the contact holes 17 and 21 of the gate pad 18 and the data pad 20 are patterned using a ninth mask pattern to expose their respective Al layers 42. This patterning produces an aluminum structure for connecting the gate pad 18 and the data pad 20 to the driver IC chip by means of the aluminum wire bonding technique having a large adhesive strength.
As described above, the conventional method of fabricating the thin film transistor substrate for the X-ray detector requires a nine step etching process, each step using a different mask. Thus, this conventional method is disadvantageous in view of production, throughput and cost.
An advantage of the present invention is to provide a method of fabricating a thin film transistor substrate for an X-ray detector that reduces the number of steps in an etching process to improve throughput and reduce cost.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
In order to achieve these and other objects of the invention, a method of fabricating a thin film transistor substrate for an X-ray detector according to an embodiment of the present invention includes the steps of forming a gate line, a gate pad and a gate electrode of the thin film transistor simultaneously on a certain substrate; providing a gate insulating layer; forming a semiconductor layer of the thin film transistor; forming a data pad, a data line, source and drain electrodes of the thin film transistor and a ground electrode simultaneously; forming an electrode for a charging capacitor; providing an insulating film for the charging capacitor; forming an electrode for preventing an etching of the insulating film for the charging capacitor; forming a protective film for protecting the thin film transistor; forming contact holes in the protective film; and providing a pixel electrode.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.